Yes size matters. You would need a tube that fits inside and can fill up all that space. Most tubes have sizes that you can use them for listed on the box or something and from experience a tube for a 23mm would work for a 25mm tire. Just get a "road" tube and make sure it is 700c and not 650c.
Better companies generally make tubes that are a little lighter. Unless you are racing professionally, it does not matter at all. Wal-mart tubes would work just fine.
EDIT: I basically meant don't get a 26" mtb tube.
Last edited by z415; 05-09-07 at 01:14 AM.